Diagnostic Considerations
Chondromyxoid fibromas, which are found in patients in the same age group in which chondroblastomas are found, may mimic the latter radiographically and microscopically. Both types of lesions tend to have well-circumscribed lytic areas on radiographs, microscopically seen areas of immature cartilage and giant cells, and perilesional marrow edema on magnetic resonance imaging (MRI). However, chondromyxoid fibromas most often arise from the metaphysis or metadiaphysis rather than from the epiphysis (where 90% of chondroblastomas are located), are devoid of calcification, and have a characteristic myxoid, pseudolobular pattern of organization, as well as more pleomorphic stellate cells.
Giant cell tumors of bone also may mimic chondroblastomas; the epiphyseal location and histologic characteristics can be quite similar. However, the former are almost exclusively seen in patients who are skeletally mature, whereas chondroblastomas tend to arise in skeletally immature patients. Furthermore, the epicenter of a giant cell tumor lies within the metaphysis. On histologic examination, giant cell tumors have elongated cells that are clustered together, in contrast to the round or polygonal cells of chondroblastoma. Calcifications and chondroid matrix also are absent in giant cell tumors.
Eosinophilic granuloma is a lesion found in young patients that may appear in rare instances as a radiolucent epiphyseal lesion similar to chondroblastoma. However, microscopic examination reveals a more heterogeneous collection of cells, including histiocytes, granulocytes, and eosinophils.
Chondroblastomalike osteosarcoma may be confused with chondroblastoma. [16]
Finally, clear cell chondrosarcoma may have features that overlap those of chondroblastoma, but the presence of large cells with abundant clear cytoplasm and vesicular nuclei, as well as type II collagen and malignant chondrocytes, should distinguish this tumor. Typically, clear cell chondrosarcoma is an epiphyseal tumor of adulthood.
Although an epiphyseal or apophyseal location is classic for chondroblastoma and extension into the metaphysis may be seen, purely metaphyseal or diaphyseal chondroblastomas have been reported. A series of seven such cases suggests that they follow the same pediatric age distribution as their classic counterparts and, apart from their unusual location, have similar radiographic features, including extensive perilesional edema on MRI. [17] Biopsy is still required to confirm the diagnosis, and treatment remains the same.
Differential Diagnoses
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Radiograph of epiphyseal lesion (hip).
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Radiograph demonstrating tumor on both sides of physis (humerus).
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Bone scan.
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Magnetic resonance image of a hip showing lobular pattern of chondroblastoma.
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Histology of chondroblastoma.
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Chondroblastoma histology demonstrating chicken-wire calcifications.
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Axial computed tomography scan of the pelvis demonstrates a lesion of the femoral head without noticeable internal matrix production. The epiphyseal location of the lesion is a clue to the correct diagnosis.
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Plain film of the hip shows a femoral head with a lytic lesion with surrounding sclerosis in the epiphysis of the proximal femur. Internal matrix formation is not present, but that finding can be a feature of this tumor.
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Coronal T1-weighted sequence shows a lesion of the epiphysis with medium signal intensity. Small islands of matrix are noted.
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Low-power photomicrograph demonstrates islands of hyaline-type cartilage, which can often be seen in chondroblastomas.
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Medium-power photomicrograph with lobules of chondroid matrix. In these lesions, the cartilage can be eosinophilic, with superficial resemblance to osseous matrix. Correlation with the radiologic studies is often helpful when in doubt.
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Medium-power photomicrograph demonstrates secondary cystic changes, which can often accompany chondroblastomas. Careful sampling of the tumor will show the correct etiology for the changes noted here.
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Giant cells are a component of this tumor, and in areas that are rich in giant cells, sampling will show the chondroblastomatous portions of the tumor.
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Immunohistochemistry for S100 is positive in chondroblastomas and is often helpful, especially when the tissue sample is small.
